Differentiated Services Code Point (DSCP) overview
Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2
Differentiated Services Code Point (DSCP) overview
Differentiated Services Code Point (DSCP) is a field in an IP packet that enables different levels of service to be assigned to network traffic. This is achieved by marking each packet on the network with a DSCP code and appropriating to it the corresponding level of service.
DSCP is the combination of IP Precedence and Type of Service fields. In order to work with legacy routers that only support IP Precedence, DSCP values are used because they are compatible with IP Precedence fields. For more information, see RFC 2474 at the RFC Editor Web site.
How DSCP works
Quality of Service (QoS)-enabled programs request a specific service type for a traffic flow through the generic QoS (GQoS) application programming interface (API). The available service types are:
Guaranteed service
Guaranteed service provides high quality, quantifiable guarantees with bounded (guaranteed minimum) latency.
Controlled load service
Controlled load service provides high quality, quantifiable guarantees without bounded latency.
DSCP is a six-bit field carrying the default values that are displayed in the following table. The equivalent IP Precedence and IEEE 802.1p values are shown in separate columns.
| Service Type | DSCP | IP Precedence | IEEE 802.1p |
|---|---|---|---|
Network control |
30 |
6 |
7 |
Guaranteed |
28 |
5 |
5 |
Controlled load |
18 |
3 |
3 |
All other traffic |
0 |
0 |
0 |
Notes
The network control service cannot be requested through the GQoS API. However, it can be requested by network management applications that use the traffic control (TC) API.
Default DSCP values can be edited remotely using Group Policy.
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